Well-dressed lawyers hustle into a new glass-enclosed building on one end of Northern Ave. Halfway down the main drag, a construction crew puts the finishing touches on Legal Sea Foods’ new flagship restaurant. At the avenue’s eastern endpoint, asbestos workers in white Hazmat suits pick clean the skeleton of an unused factory to prep it for its demise. The South Boston waterfront. The Seaport District. The Innovation District. Call it what you want. If you visited Southie’s northern shoreline on a recent winter’s day, you would have seen that the area’s long-awaited redevelopment is finally taking shape. The waterfront — with its windswept lots and rows of parking meters — was often viewed by commuters as just a cheap place to park. But that’s about to change.